The present invention relates to a cooking hood used in making a cake in a microwave oven and a method for making a sponge cake by use of the cooking hood.
A microwave oven is used to heat and cook a foodstuff by the frictional heat generated when the microwaves emitted from the oven act on the moisture in the food. Because foods can be cooked more quickly with a microwave oven than with any other cooking means, an increasing number of people now use it.
One problem with a microwave oven is that the food in the oven is more difficult to heat at its central portion than at its peripheral portion. This is because a microwave oven has such a structure that the microwave density is the lowest at the central portion. Most of the microwaves tend to be absorbed in the moisture present near the periphery of the material to be cooked and thus are prevented from penetrating deep into the material. Thus, the peripheral portion tends to be heated sufficiently before the heat generated at the peripheral portion is transmitted to the central portion.
Because of the abovesaid problem, the use of a microwave oven has heretofore been limited to defrosting, reheating and some applications in which the food is not likely to undergo a change of taste even if heated unevenly.
But, because of the advantage of microwave ovens in that foods can be cooked quickly and offhandedly, various methods have been proposed to solve the abovesaid problem not only by manufacturers of microwave ovens but also by professional cooks.
As described above, a food is heated in a microwave oven by the heat generated by friction between the particles in the food. Thus, when baking a cake in a microwave oven, for example, it is necessary that its dough contains more moisture than when baking a cake in a gas or electric oven.
Although the heat transfer coefficient may increase if the dough contains a large amount of water, the moisture in the dough near its periphery will absorb the microwaves actively, thus decreasing the microwave density in the central portion. This will cause the peripheral portion to be heated quickly and the central portion to be heated much more slowly, widening the difference in temperature between the peripheral portion and the core portion. This means that even when the dough is heated to such an extent that its peripheral portion is well-done, its core portion is still half-done, whereas when the dough is heated until the core portion is well-done, the peripheral portion has been overdone and has hardened.
It has been a common practice to form a center hole in the dough (or shape the dough into a doughnut) to prevent this problem. But a sponge cake having such a center hole could not be used as the base for a decorated cake.
If the water content of dough is increased to a given level, the heat transfer coefficient will increase to such an extent that the core portion and the peripheral portion will be heated substantially uniformly in spite of the difference of microwave density therebetween. But because the gluten in the dough can absorb only up to 60-65 per cent of moisture, any excess water in the dough will make the dough sticky. The stickiness of the dough will disappear if heated for a prolonged period of time. But the cake thus made will be less tasty. The optimum heating time in a microwave oven is said to be 4 minutes at 500 watts or 3 minutes and 50 seconds at 600 watts. These values vary more or less with the oldness of the oven and the length of the power cord.
A cake-making powdery material is now commercially available which contains flour, sugar, egg and the like in a mixed state and which is adapted to be cooked in a microwave oven. According to its cooking directions, water (or milk) has to be added by as much as 60 per cent by weight of the material. The cake made from dough containing such a large amount of water or milk cannot be tasty.
Another proposed cooking method teaches to cover cake dough nearly hermetically with a hood, sheet or cloth to prevent heat dissipation and thus improve the heating efficiency. But with this method, the dough will be baked as if in a casserole, and the resulting food would not deserve to be called a cake.